1. Field Of The Invention
This invention relates generally to couplings constructed to be quickly connected to a cylindrical member, and more particularly, but not by way of limitation, to a coupling for quickly connecting fracturing equipment, a plug container or the like to a casing of an oil or gas well.
2. Description Of The Prior Art
The most common manner in which fracturing equipment, cement plug containers, or similar equipment is connected to the upper end of a well casing is by use of a threaded nipple which has a threaded lower end compatible with an internal thread of a conventional casing collar. This nipple and the associated equipment are attached to the well casing by threading the threaded nipple into the threaded casing collar.
Numerous problems have been encountered when utilizing threaded nipples to connect such equipment to a well casing.
Often the casing stands as much as fifteen feet above the floor of the drilling rig thus creating a hazard to personnel who attempt to work at that height to perform the threading operation.
Also, due to the difficulty of the threading operation, the use of a threaded nipple is susceptible to cross-threading which can lead to blowouts.
Another problem encountered with using threaded nipples is the difficulty in achieving the recommended torque values for makeup of the threaded connection. Casing threads are designed to be made up with extremely high torques. For example, optimum recommended torque values for 51/2-inch, eight round, long thread casing range from 2400 ft-lbs. to 8900 ft-lbs. depending on the weight and grade of the casing. Since the casing string joints themselves are made up with power tongs on the drilling rig, recommended torque values can easily be achieved when assembling the casing itself. However, when rigging up for fracturing services or the like, power tongs are normally neither available nor compatible with the equipment being attached to the well casing. Consequently, change-over adapters for fracturing equipment must be made up by hand with chain tongs and it often is very difficult to achieve the recommended torque values for the threaded connection.
These problems with the use of threaded nipples for connecting equipment to a well casing have led to numerous attempts to construct a clamp-on type of connection for attachment to the well casing.
One such attempt is shown in my pending U.S. patent application Ser. No. 296,325 filed Aug. 26, 1981, entitled Quick Connect Coupler which itself is a continuation-in-part of my prior U.S. patent application Ser. No. 238,802 filed Feb. 27, 1981, and now abandoned. Although my co-pending application is not itself a prior art reference to the present application, apparatus substantially like that illustrated in FIGS. 1-7 of my co-pending application has been commercially used by the assignee of the present invention more than one year prior to the filing date of the present application, and thus the structure illustrated and described with regard to FIGS. 1-7 of my co-pending application does constitute prior art with regard to the present application.
The apparatus of FIGS. 1-7 of application Ser. No. 296,325 was particularly disclosed with regard to the connection of a cement plug container to the top of a well casing having a threaded collar at the upper end of the casing. That coupling included a body member and annular seal means for sealing between the body member and the casing collar. A plurality of collet sections were disposed around the body member and each of the collect sections included an upper end connected to the body member and a lower end adapted for engagement with a lower end surface of the casing collar. An outer sleeve was slidably disposed about the plurality of collet sections and was slidable relative to the collet sections between an open position wherein the lower ends of the collet section could receive the casing collar therebetween, and a closed position wherein the body member was sealingly coupled to the casing collar.
In the coupling member of application Ser. No. 296,325, the compressional seal between the casing collar and the body member was achieved through a cam action created by an upward force on the actuating sleeve. Thus it was necessary that the actuating sleeve be raised by something other than manual power in order to provide the necessary force.
Also, the apparatus of application Ser. No. 296,325 did not provide for any adjustment in order to accommodate differing lengths of casing collars, but instead provided only for accommodation of casing collars having a length within a relatively narrow band. This accommodation was provided due to longitudinal compressibility of the seal between the body member and the casing collar.
Another prior art device for coupling well equipment to a well casing is disclosed in pending U.S. patent application Ser. No. 374,869 of Brisco filed May 4, 1982. That application is entitled Coupling Device, and is assigned to the assignee of the present invention.
The Brisco device used a locking collar having first and second pivotally connected arcuate collar portions to engage the lower surface of the casing collar. The Brisco device was adjustable to accommodate any length of casing collar, and this adjustability was provided by the use of a cylindrical adjusting nut having an internally threaded upper end threadedly engaged with a threaded outer surface of a body member of the device to be attached to the casing. The cylindrical adjusting nut was connected to the locking collar so as to move the locking collar relative to the body member.
The upper end of the casing collar in the Brisco device was closely received within a bore of the body member. A main seal means was disposed in the bore of the body member and included an outer seal against the bore of the body and a lower main seal for sealing against the upper end of the casing collar. This main seal was hydraulically biased against the casing collar.
One problem with the Brisco device is that the locking collar, which has a C-shaped cross section, carries the loads between the body member and the casing collar substantially through bending type loading of the C-shaped collar. The C-shaped collar attaching device of Brisco creates certain difficulties in design since it is more difficult to analyze through conventional design techniques, and also it is more susceptible to failure due to surface imperfections and the like than is a device which carries the loading primarily through tension.
Thus, although the prior art has recognized the general problem addressed by the present invention, namely that of providing a reliable quick connect coupling for attaching well equipment to a well casing having a threaded casing collar at the upper end thereof, there is still a need for a more reliable device which also has the flexibility of accommodating casing collars of different lengths.